Re: SATA-performance: Linux vs. FreeBSD

[Alan <alan@lxorguk.ukuu.org.uk>]

> Well they do. The Flash disk I have (SATA-I) is capable of 48 MB/s and this 
> value is reached over the whole disk size by windows as well as by FreeBSD. 
> See my test results in the first thread.

Ok a flash disk should be more stable

> My Seagate Barracuda Harddisk drive (SATA-II) starts with 76 MB/s and 
> decreases linearly to 35 MB/s due to the fact that it has to write to a 
> rotating disk. But on a flash disk there is nothing rotating...

The hard disk one isn't guaranteed or stable but the flash especially if
it is aimed at it ought to behave.

> So where is the difference between SATA-I and SATA-II ?

All physical side if they are on the same controller when you do the
tests. Mostly latency,

> And why is FreeBSD able to write with constant rates (the complete 25 GB, all 
> with 48+/-0.1 MB/s) but Linux 2.6.18 not ?

Does the FreeBSD fsync sync to media ? Also what controller is being used
here, and do you have EHCI USB support running ?

> With a dedicated (rotating) SATA II device, using the first 70% of disk space 
> no problem -- tested ! With a SATA-I device only a problem with Linux 2.6.18

I suspect the SATA-1 itself may not be the decider but something else -
eg the hard disk using NCQ, which would cover up any latency related
problems.

> Journaling of data: you are right, ext2 performs better than ext3.

And ext3 in writeback mode ought in theory (but practice is always
harder ;)) be faster than ext2.